The present invention relates to interbody fusion devices disposed between two bony structures to maintain spacing therebetween and promote bony fusion. More specifically, the present invention relates to interbody fusion devices having threads or other structures defined on the outer surface to limit movement of the device between the bony structures. Most often, such devices find application in the spine for fusing adjacent vertebrae.
It is well known to utilize an artificial spinal fusion implant to be inserted in the space between two adjacent vertebra after removal of a damaged spinal disc or portion thereof. Common forms of such devices may be configured in a substantially cylindrical configuration. These cylindrical configurations can include truncated sidewalls or a tapering body portion. However, for bone fusion to occur, the invasion of new delicate blood vessels from the adjacent healthy bone is necessary for the creation of new living interconnecting bone. Motion around the implant can restrict or even prevent bone healing. Therefore, it is important to stabilize the implant upon insertion. In most applications, the outer body of the fusion device is provided with one or more structures to resist repulsion from the disc space when a load is applied to the spinal column. For example, U.S. Pat. No. 5,015,247 issued to Michelson discloses substantially cylindrical interbody fusion devices with an external thread disposed on the outer surface. The thread is interrupted at various locations. Further, the trailing portion of the thread may be twisted slightly. This twisted portion of the trailing edge acts as a locking thread to resist subsequent unscrewing of the fusion device. While such interrupted locking threads may be satisfactory in preventing unscrewing, the manufacturing process of twisting each of the individual teeth to create a locking thread may be costly and difficult to control from a quality aspect.
Thus, there remains a need for an improved interbody fusion device that incorporates features to resist undesired rotation after implantation while at the same time simplifying the insertion of the implant into a human body and minimizing manufacturing complexity.